The invention was developed for use in stormwater drainage systems, and combined sewer systems (some older US cities have combined sanitary and stormwater sewers). These sewers are designed and constructed to convey water from a developed area into natural receiving water or other destination. When storm sewers were first constructed, the goal was to remove the water from the developed area and convey it into the receiving water as quickly as possible. At that time, no attention was paid to the potential for pollution from stormwater runoff.
During the last twenty years, stormwater runoff has been identified as a significant source of pollution in waters of the United States. The stormwater runoff from a developed area (a parking lot, for example) can contain oils and other fluids from leaking cars, zinc and heavy metals from brake pads and other sources, nutrients from fertilizers and air pollution, sediments, and garbage and other debris. All of these constituents impact the receiving water that the stormwater drainage system discharges to.
In addition to these pollutants, many older US cities have combined sewer systems, in which the sanitary sewer drainage and stormwater runoff are conveyed in the same pipes. These systems function perfectly well when the weather is dry, but have the potential to overflow during large storms. Because wastewater treatment plants are designed to handle limited flows, even frequently recurring storms have the potential to exceed the treatment capacity of the plant. These cases are termed combined-sewer overflows (CSOs).
With the reauthorization of the Clean Water Act, Congress gave EPA the authority to regulate discharges to waters of the United States from larger stormwater drainage systems, including CSOs. Over the last four years, the scope of the regulation has been increased to include many medium sized and small stormwater drainage systems as well. In response to increasing regulation and federal oversight, a demand exists for devices which are capable of removing stormwater-specific pollutants from a flow stream.
Other technologies, including BaySaver's patented physical separator (U.S. Pat. Nos. 5,746,911 and 6,264,835), rely on gravity settling and sedimentation to remove suspended sediments, oils, and other floatable debris from stormwater runoff. These systems, while effective at low flow rates, often include a bypass structure that allows high flows to pass through or around the system untreated. Although the runoff during intense storms usually has lower concentration of pollutants like sediments, nutrients, and oils, there is often a significant amount of trash, debris, and other floatable material entrained in the water. The present invention is intended to remove these constituents from stormwater or CSO runoff and retain them in a structure so that they can be easily removed during routine maintenance.
The prior art used for this purpose includes several US-patented systems. These systems often rely on vortex technology and hydraulic flow controls to enhance the removal of contaminants from the influent water, and many of the existing systems include. multiple outlet streams: a single outlet for treated effluent, and a second outlet for contaminated flow.